Nowadays spot lighting devices are applied largely in retail lighting and museum lighting. The light distribution is mainly defined by the light source and the optical solution, i.e. an optical part, such as a reflector, TIR-collimator or lens. Each optical solution has its own properties, advantages and disadvantages and the choice for the optical architecture largely depends upon the requirements of the application.
A TIR-collimator, for example, is a solution with high optical efficiency and reasonable control on the light distribution, but it cannot make a variable beam width. A reflector can be a solution with good optical efficiency for wider beams, but due to the direct light, it usually doesn't show a clear cut-off in the light distribution. To a certain extent, this can be improved by a deep reflector or by shielding the direct light, but this will reduce efficiency and very narrow beams still remain challenging. Fresnel lenses tend to render less uniformity of light distributions because of the occurrence of diffraction at the edges of the refractive/reflective rings. Narrow beams with good intensity distribution can be made using a convex, positive lens, but has the disadvantages that it will show chromatic aberrations and a visible image of the light source. In addition, for example when a LED is used as the light source in combination with such a positive lens, the risk on a relatively low optical efficiency is increased, because some light from the Lambertian LED-source will not enter the lens, but it will be absorbed in the housing. The width of the beam can be modified by adjusting the distance between the lens and the LED.